I'm trying to write an ANTLR4 grammar for a language with a low precedence
postfix operator (Wolfram Language with '&', but I use a simple toy grammar
below). I'm struggling with finding the right pattern to express this
language.

The problem with this grammar is that the generated parser chokes on, for
example, the input '2++^3', as '^' cannot follow '++' in this grammar. If I
get rid of implicit multiplication I can collapse the grammar into a single
rule that parses the language I am wanting, but I don't want to give up
implicit multiplication.

What's the pattern for this situation?

Incidentally, this is my first post to this group, and I am charmed to see
several authors of my textbooks among the members here.